Have a secondary hard-drive in your laptop/desktop that you don't often use?
hd sleeper is a small, free and open-source utility for Mac OS X 10.6+ that will allow you to quickly put to sleep and wake up your hard-drives.

With many people switching over to SSD these days, I wanted a quick way to put the secondary hard-drive to sleep when not in use, to save energy and create less noise.
hdsleeper is the result, it seems to work decently so I've decided to share it.